Plate lifting device



'7 Sheets-Sheet 1 Filed Jan. 22, 1957 Byt'/ll? C /CE ATTORNEY June 2l, 1960 J. D. NOBLE ET AL 2,941,675

PLATE LETING DEVICE Filed Jan. 22, 1957 '7 Sheets-Sheet 2 JAG/r 0 NOBLSNVENTORS G50/EGE' WA m15 BENTLEY EDGAR c. /05

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ATTORNEY June 21, 1960 J. D. NOBLE ETAL PLATE LIFTING DEVICE Filed Jan. 22, 1957 l'7 Sheets-Sheet 3 'JAG/r o.

ATTORNEY June 2l, 1960 J. D. NOBLE ETAL 2,941,675

PLATE LIFTING DEVICE Filed Jan. 22, 1957 r7 sheets-sheet 4 El. -J-

d c ,65 4/ /f 4 SVE- sa 1 6 72 jh I 60 6 1 2'8 Ll i/fl- ///////////////////5fl L cln- .5l 53 I INVENTORE)` JACK 0. NOB/ E GERGE WAY/VE BENTLEY ATTORNEY J. D. NOBLE ET AL PLATE LIFTING DEVICE June 21, 1960 7 Sheets-Sheet 5 Filed Jan. 22, 1957 INVENTORS JAG/f D. NOBLE GEORGE WAYNE' BENTLEY BYEDGAR C. Z/GE Z A TTOR/VEY June`2l, 1960 J. D. NOBLE ErAL 2,941,675

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INVI'NTORf'` JACK D. NOBLE GERGE WAY/VE BENTLEY By Eos/m c. mae

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PLATE LIFTING DEVICE Filed Jan. 22, 1957, Ser. No. 635,172

Claims. (Cl. 212-14) This invention relates to improvements in plate-lifting devices such as traveling cranes for transferring steel plate one at a time from a stack to a conveyor line. More particularly, it relates to a type of lifting and transporting devices employing vacuum cups.

Devices of thisV general type have many applications in industry. For example, large stacks of steel plate may be deposited in a chosen location, and the machine of this invention will then pick up each plate, one at a time, by its suction cups, will move along a trackway to a position remote from the stack and deposit the plates, one at a time, in sequence on a conveyor belt, leading into a shearing machine. Similar machines may pick up the plates from a conveyor belt and deposit them on a stack. In fact, there are many applications of the invention.

In machines of this type, which heretofore employed vacuum cups, certain serious difficulties had arisen. The vacuum cups are supported on a frame that is driven up and down in the machine by power, for descending to contact the plates and ascending to carry them, etc. When the cups came down from an elevated position, it often happened that the power drive failed to stop the frame on contact with the plates, and the power continued to move the cup-supporting frame relative to the remainder of the machine. If the frame was pushed far enough, the entire machine was lifted off the track. With a stack of plates for instance, the machine would have to go down to a slightly different level each time, lower by the thickness of the removed plates. The adjustment of height was very critical, and when the machine was lifted ott the -track, it often did not come down squarely on the track again or missed it entirely, so that operations would have to cease while a very large crane was brought into position to lift the entire machine back on to the tracks.

Similarly, when the adjustments were not exactly right, instead of going too far, the cups would as likely not be lowered far enough to obtain a sealing engagement with the plate. Then, when the cups were raised, they would drop the plate. This not only created loud noises and great inconvenience, but ymeant that someone had to be in constant attendance to make sure that the machine, which otherwise could have been operated automatically, would continue to engage in the right position on each cycle.

An additional problem arose from the fact that the plates are not always absolutely flat, and therefore there were circumstances `in which some cups would satisfactorily engage the plate, but others would not. In that event, the plate was carried along with one corner or one side sagging, and sometimes struck objects which the machine was supposed to raise the plates over. The plate was sometimes knocked off and damaged or the object over which the plates were to be lifted was damaged.

All these problems have been solved in the present invention by providing a novel structure in which the plurality of cups are spring mounted, and in which a limit switch is provided, adjusted so that the machine will Stte atent O ICC lower the cups to their contact position and then compress them against the pressure of the springs for an uncritical short distance before stopping the vertical downward movement of the frame and turning on the vacuum pump. This structure has, therefore, insured that all four cups make a perfect sealing contact with the plate, and at the same time prevents the frame from going down so far as to lift it olf the track.

It is, therefore, an object of the invention to provide a sheet-handling crane employing vacuum cups in which the sealing engagement of all of the plurality of cups is insured by a resilient yielding mounting of the cups.

Another object of the invention is to provide a crane for handling sheet material in which a plurality of vacuum cups are mounted in combination with a limit switch so as to insure engagement of the cups while at the same time preventing the frame supporting the cups from descending so far as to raise the crane olf its tracks.

Another object of the invention is to provide an arrangement by which the vacuum cups may be disposed to best advantage for lifting both wide sheets of material and relatively narrow strips.

Another problem has been that either leakage of one cup or faulty engagement of just one cup has often not prevented the sheet from being lifted, and the sheet has been carried with one corner down, where it could strike something and cause damage or be damaged. Another object of this invention, therefore, is to solve this problem by providing means to prevent lifting unless all the cups are at the proper vacuum conditions.

Other objects and advantages of the invention will appear from the following description of a preferred embodiment thereof given in accordance with 35 U.S.C. 112.

In the drawings:

Fig. l is a view in end elevation of a crane embodying the principles of the present invention, the crane being shown having four suction cups lifting a piece of heavy steel plate.

, `Fig. `2 is a view in side elevation of the machine of Fig. l, again showing the machine in its elevated position with the steel plate `lifted into carrying position. A portion of the frame is broken away to shown the parts behind.

Fig. 3 is a view in side elevation and in section on a reduced scale as compared with Fig. 2, showing the device in its lowered position, and with certain parts broken away in order to show the others more clearly.

Fig. 4 is a plan view in section taken along the line 4-4 of Fig. 3, on an enlarged scale as compared with Fig. 3. In broken lines is shown an alternative position of 1the suction cups, used when lifting narrow strip materia Fig. 5 is a view in elevation and partly in section on an enlarged scale of one of the suction cup units of Figs. 1-4.

Fig. 6 is a plan view in section, taken along the line 6 6 in Fig. 5 and shown on a reduced scale as compared with Fig. 5.

Fig. 7 is a top plan view of a portion of the device showing the rotatable mounting of the yoke linking a pair of suction cups, by which the suction cups may be shifted from the Fig. 4 solid-line position to the Fig. 4 brokenline position.

Fig. 8 is a view in elevation of the portion shown in Fig. 7.

Fig. 9 is a view in elevation of a modified form of suction cup unit.

Fig. 10 is a simplified electrical circuit diagram of a modified device having the safety control shown in Fig. 9 at each cup.

Fig. 11 is a simplified across-the-line electrical circuit,

diagram of the control apparatus.

A crane 1t) embodying the principles of the invention is shown most completely in Figs. l and 2 and includes a main frame 11 with four depending legs 12, 13, 14, and one not shown. Each longitudinal pair of legs (e.g., 12 and 13) is joined by a lower frame member 15, and each leg yis supported von a wheel .16, preferably of the type flanged to ride on `a track 17. A least one of the wheels, and preferably va pair 12, 14 as shown in Fig. 1, are driven through ya chain drive 18, 19, the power being supplied by an electric motor 20 or other similar vdevice mounted on a top portion 21 of the main frame 11.

.In addition to the main frame 111 the device is provided with a lifting or cup-supporting frame 22 which is adapted 'to be raised and lowered within, and to be .sup ported by the mainframe 11. VThis lifting frame V22 may comprise principally a longitudinally extending beam 23 of great strength, to which .is secured a vertically extending rack beam 24. Pinion means 25 are provided on the top 21 of the frame member 11, together with driving means 26, such as a chain and sprocket arrangement, 'and a motor 26a for rotating the pinions 25 so as t raise and lower the rack 24 and thereby raise and lower the lifting frame 22.

Along one side of the longitudinal frame member k23 may be mounted a pipe 30 and adjacent the center, preferably connected by a swivel joint 31, a generally vertically extending pipe 32 joins the horizontally extending pipe 30. Through a suitable arrangement, such as threeswivel joints, the'pipe 32 is connected to a suction pump or compressor 33 so as to' provide a low pressure within the pipes 30 and 32 at lifting times. As will be ,explained `later,'the pump 33 is always running during operation of the unit, and a pressure switch A34 of the .vacuum type is actuated at a predetermined -line pressure (vacuum) to actuate the lift mechanism for raising the frame 22 and its associated parts.

At each of the two outer extremities of the frame member 23 is provided a rotatable connection 35 for each of a pair of endV frame members 4G extending trans versely of the horizontal beam 23. The members 40 may be pipes, preferably to provide as an integral'part thereof conduits '41 adapted for connection by a flexible conduit 42 with the main longitudinally extending pipe Si?. A stationary disk 36 of the connection 35 over'- lies and supports a rotatable disk 37 that is part of the frame member 40. A lever y38 is piyotably mounted at 39 to release for separa-te movement (dotted-line position, Fig. 8') or toM lock together (solid lines in Fig. 8) the disks 36 and 37. Depending vertically from each outer end of each transverse frame member 40 is a suction cup mounting member 44 from'each of which depends a suction cup `45 that is used to seal against the steel plate 46 and hold it while ,it is raised and transported.

As shown in Figs. and 6, thesuction cup assembly 45 includes at the lower end a flat disk 5,0 to the lower surface 51 of which is secured (as by'bolts 5(2)V an annular clamp 53 compressing between its stepped outer periphery 54 and the stepped inner periphery 5.5 of the disk'Stan annular rubber cupV member y56. This Vstructure makes it unnecessary to provide a solid rubber disk, since sealing contact between the disk 5t) and the rubber ring 56 is assured by the tight clamp 53r and the peripheral edge 57 of the rubber is allthat is needed to obtain a sealing contact with the steelvplate 46 to be lifted. Moreover, the annular clamp '53 prevents the rubber cup member 56 from blowing in, backing it up at all times.

The 'steel disk 5t) may be secured, as by welding, to a lower universal joint member 66 which in turn fits into an upper support member 61 by means of the universal joint 6 2. The upper member 61 is secured to a large threaded bolt 63 thatis slidably mounted in a bore 64 through theV cup-supporting frame member 44.

An important feature of the present invention is the springmountingof the va'cuum cup assembly 4 5. .For

this purpose, a cylindrical recess 65, stepped outwardly from the bolt-receiving bore 64, may be provided in the lower end of the frame member 44 and a spring 66 may be mounted between the shoulder 67 of the recess 65 and the upper support member 61. This makes it possible for the cup 45 to engage a plate 46 to be lifted and to come into sealing contact with it and then for the frame 22 to move down further relatively to the suction cup 45 without depressing the suction cup 45 to any great extent, and without raising the main vframe 1i orf the track 17. The importance of this feature will be seen later on in the description of the operation of the device, out it should be stated here that it does, in connection with the universal joint 62, assure engagement of the cup d5 with the plate 46, even if the plate 46 should be nent or otherwise not perfectly flat, and it does allow for an uncritical amount of movement between the lifting frame 22 and the suction cups 45 without any harm to the device.

Into a threaded opening 68 :through the disk 50 is threaded the lower fitting 69 of a valve 70 Whichis preset to a desired valuevfor the suction or which can be closed oi when fewer cups 45 are to be used, so as to enable suction to be obtained in the ones used. vAV flexible conduit 71 leads from this point up to the main transverse conduit 49, the exible conduit permitting the relative movement between the main conduit 40 `and the valve 70 when the spring 66 is compressed, For the sake o f adaptability, etc., a hand-operated stopcock valve 72 may be provided for individually closing oi the conf duit 71 at the valve '70 and for regulating the pressure at this point to any desired amount.

In the form of the invention shown in Figs. 1*-6A a limit switch is attached at a general central location to the lifting frame 2,2. The switch Si) may be connected by a exible conduit 81a to Ythe driving motor,

26a for raising and lowering the lifting frame 22. `The limit switch Si) includes a lever member 81 which enf gages the steel plate and thereby actuates 4the switch 50. The height of this limit switch S0 is set so that `it will not be engaged until after the cups 45 have been fully engaged and have partially compressed the springs 6 6. It is desirable to have the springs 60 compressed J"somewhat after engagement of the cups 45 to permit a slight amount of end movement and thereby not make mounting of even this portion critical, but normally engagement of the limit switch 80 will instantly shut ,offV

the device since it shutsY oi the motor ggg wpihdrivg the rack 24 and pinion 2 5 v Y.

Explanation of the circuit diagram of Fig. 1I

The simplified circuit diagram of Fig. 1l shows a circuit that may be used in conjunction with the abovedescribed apparatus. The circuit is shown in across-thee line type of diagram, and it will be described beginning at the Vtop line 200. In therline 260, the motor 2Q is shown connected for reverse speed operation through a normally closed relay-operated switch 291, a normally open relay-operated switch 202, and automatic contacts 203. Au are always closed during automatic operation of the device by the closure ofuthe manually operated switchV contacts 291 in the bottom line 290.)

In the second line 210, the forward-speed contacts of the motor 20 are connected in series with normally open (The contacts 203 and all other contacts'labeled open mechanically operated switch 232and Au contacts 233. 'Ihe symbol R2 has also been placed above the contacts which it controls, namely, the normally open contacts 211 and normally closed contacts 273.

Line 240 contains a third relay 241, identified also by the symbol R3 as are the normally closed contacts 212 and normally open contacts 264 which it controls. The .relay 241 is in series with normally closed mechanically actuated switch 242 and Au contacts 243. A fourth relay R4 is in line 250 where it is identied by reference numeral 251 and is in series with a normally open mechanically actuated switch 252 and Au contacts 253. The symbol R4 has also been placed over the normally open contacts 202 and normally closed contacts 275, which it operates.

Downward travel of the frame 22 is controlled by line 2,60 wherein the down contacts of the motor 26a are in series with two parallel lines 261 and 262. The line 261 includes normally open R1 contacts 263 that are actuated by the R1 relay 221 and Ialso includes the normally closed limit switch 80. The line 262 includes the normally open R3 contacts 264, which are operated by the R3 relay 241, and the normally closed contacts 265 of a second mechanically actuated limit switch. Both lines 261 and 262 are in series with Au contacts 266.

Upward travel of the frame 22 is controlled by line 2,70 where the up contacts of the motor 26a are in series with two lines 271 and 272. The line 271 includes normally closed R2 contacts 273 operated by the R2 relay 2 31 and also includes the vacuum switch 34, and a timedelay relay 274 which is controlled by the opening of the normally closed limit switch 80. In line 272, normally open R4 contacts 275 operated by the R4 relay 251 are in series with a time-delay relay 276 actuated by the opening of the normally closed limit switch 265. Both lines 271 and 272 are in series with Au switch contact 277.

The vacuum pump 33 is in line 280 in series with Au contacts 281. In line 283, a bleed valve 284 has its solenoid control in a position normally closing the valve 2,84, but when contacts 285 are closed by the limit switch 265, the pneumatic circuit is bled to drop the sheets of plate 46. Au contacts 286 are in series with members 284 and 285. The main automatic control switch 291 is in the line 290. Closure of the automatic switch 291 by hand initiates automatic operation by closing all of the Au contacts 203, 213, 223, 233, 243, 253, 266, 277, 281, and 286.

Operation of the electrical circuit as well as operation of the remainder of the ydevice is explained in the following section.

Operation of the device of Figs. 1-8

In the operation of the device, it will be assumed that the main frame 11 is track mounted to move between two positions and that it will be lifting a steel plate 46 from one position and depositing it at the other position. The cups 45 may be set in a single line for narrow strip material (as shown in broken lines in Fig. 4) or in a rectangle for wider sheets (as shown in solid lines in Fig. 4). With the machine in a neutral position, 'for example only, the frame will be moved by its driving motor (moving in reverse, as actuated by the line 200 when the relay contacts 201 and 202 are closed, as well as the Au contacts .203) and chain drive 18, 19 to the position immediately above a stack of steel plates 46 when, either by the action of an operator or more normally by an automatic switch 222, its lateral movement along the tracks 17 will be stopped. Engagement of the switch 222 opens it and de-energizes the R1 relay 221 so that thenormally closed R1 contacts 201 `are opened and the normally v closed R1 contacts 263 are simultaneously closed. At the same time that the motor 20 is stopped, therefore, the normally open switch contacts 263 are closed which actionk starts the motor 26a driving the pinion 25 `and 6 t therefore lowering Ithe rack 24 and with it the lifting frame 22 with its four suction cups 45 and the limit switch 80.

This lowering continues until the four suction cups 45 engage the steel plate 46 and continues beyond that point to insure firm engagement, the springs 66 being partially depressed. That means that if the plate 46 is not perfectly level, there will still be enough lowering of the device to engage all four of the suction cups 45. It also means that this engagement takes place without any tendency to lift the main frame 11 off its tracks 17 and it means that the adjustment of the stopping position is by no means critical. When a predetermined but still uncritical lowering position has been reached, the limit switch arm 81 engages the steel plate 46, opens the switch80, and turns oi the raising and lowering motor 26a, stopping the lifting frame 22 in the stationary position with the four suction cups 45 sealed against the steel plate 46. At the Same time, through a delay relay 274 of very short time, the limit switch closes the switch 34 which is connected to the pneumatic line joining the interior of the suction cups 45 with the source 33 of suction. In other words, the compressor 33, which is always running, has produced a suction within the main conduits 30, 32, and 41, and the limit switch 80 operates a valve which connects the main conduit 41 with the interior of the suction cups 45. The resulting suction7 which isthen applied, is well able to support the plate 46 by the suction cups 45. After a further time delay of a few microseconds provided in the relay 274, the switch 34 is actuated if the desired vacuum is obtained. If there is leakage or any reason Why the vacuum level is not obtained, the machine stops as is, and the operator investigates the cause of the stoppage. This safety feature is important. Upon actuation of the switch 34, the circuit 271 is closed and the plate 46 is lifted, the motor 26a against starting; but running in a reversed position so as to rotate the pinion 25 in the opposite direction and raise the rack 24.

The rack 24 is raised until the main frame 11 is elevated and the plate 46 is in the desired transporting position, as determined under the specic operating conditions called for in the particular plant where the device is to be used. With the plate 46 in this position, the normally open limit switch 232 is engaged and closed, and this limit switch 232 stops the upward movement of the plate 46 by actuating the R2 relay 231 to open its R2 contacts 273. The throwing of this limit switch in automatic operation `also operates to start the translational movement of the machine 10 along its rails 17 by closing the normally open R2 contacts 211 and so starting the forward speed of the motor 20 driving the forward wheels 16 along the tracks 17. This driving continues until at a desired forward position the normally closed limit switch 232 is opened, stopping the machine 10 by de-energizing the R3 relay 241 to open the normally closed R3 contacts 212 for the motor 20, and starts the motor 26a by closing the normally open R3 contacts 264, to lower the lifting frame 22 and its steel plate 46 to the desired position. Upon its reaching the desired position, the limit switch 265 is thrown, automatically, as usual, cutting otf the suction current by the switch 265 acting to momentarily close normally open contacts 285 to momentarily open and then close the bleed valve 284, and when this is done, the plate 46 is deposited free of the machine 10. If it is placed on a conveyor belt, for example, it moves on. While breaking the suction circuit, the switch 265 at the same time (or through a time delay relay 276) causes the motor 26a to raise the frame 22 by completing the circuit 272. When the frame 22 reaches its upper position, it closes the normally open limit switch 252, energizing the R4 relay 251 to open the contacts 275 and stop the upward movement of the motor 26a while also closing the normally open R4 contacts 202 and to drive the motor 20 to move '7 the machine 10 in reverse'to move it along the tracks 17 back to the ,original position-wherethe lirst limit switch 222 stops it and the lifting frame 22 is again lowered to pickup another plate V46.' VThe cycle continues Vas often as may be desired, and Vmay be fully automatic.

Modified -orm of spring linkage, limit switch, and nsafety i 4 switch `rinodiiecl form V of suetion cup 100 is shown in Fig. 9. Some of the elements `are identical to those shown in Pig. Y5, and these have lreceived identical numbers. However, several important modifications are also ineluded.

TO .the Uppersideof the disk 50 is secured -a .socket member 101 having aycentralupperopeningi102. The socket member 1,02 is not welded to the disk50, however, until a Vcentral rod 1035is inserted through the opening 192, so that its ball-.like lower .end 1.04, which may be rather ellipsoidal in shape, if desired, is in place in the space 105 enclosed by the socket member 102 and the upper side of lthe disk 5,0. `l'fhe result is a hall-andsocket juncture between the disk 510 Vand rod 103 ,thatV is less expensive than the uniyersal -joint 62 and quite as effective. In f act, it may also be ltermed a universal connection.

The threaded upper-end 106 of the rod 103 extends through a yoke or frame 107 and is surmounted by a cap nut 108 with a frustoconical upper end `109. A pair of stop plates or washers 110 and 111 are secured lrespectively against the upper surface 112 kand lower surface 1,13 by bolts 114 and nut 11,5. The upper washer 110 serves as an engagement or stop vmember to limit downward movement ofthe rod 103 by engaging the lower end of the cap nut 108. An Open-wound helical spring 116 is partially compressed between the lower -washer 111 anda bottomwasher 117 that rests on top of the socket member 1,021.

flhus downward movement ,of ythe frame 22 causes downward movement of the yoke frame 107 and the cup 100 until the cup 100 engages the steel plate, and then th? CUP 10,0 and rod 103 remain Ystationary while theframe 107 continues to move down against fthe pressure of the spring 117.

In this form of the invention the limit switchi) located at the `center of lthe device is replaced by a limit switch 1 20located adjacent vone of the cups 100 and tripped by being engaged bythe vc ap nut 1G87. This gives more ac curate control, Vin that movement'by the frame 107 rela-l tive to the rod ,103 is assured by the positioning of the switch 120 on a bracket 121 above the frame '107, with its actuating roller122 thereby being spaced for apredetermined movement of theV rod 103 against the pressure of thespring 116. With the switch 80, sag of the center of the plates 46 could cause trouble, if the plates were not fully supported on a flat surface; this modification assures that such sag makes no difference, while suf.- iicient play is given to assure engagement of all -four cups 100 under any normal arrangement.

One further modiiication is shown in Figs. 9 and l0, and this one may or may not be used separately from the preceding modifications, if desired. As stated earlier, the pressure switch 34 is designed to actuate the lifting mechanism for the frame 22 only when there is sulicient vacuum in the line )to thecups 45 sothat they will hold the plate d6. But it sometimes happens that a single pressure switch 34 will be actuated even though one cup 45 is leaking. Such a cup 45 may be engaged while not providing enough vacuum to lift its corner of the plate, yet the total vacuum in the circuit may be sufcient to ectuate the pressure switch 34, due to higher vacuum in other cups 45 and to the leakage from the one cup 45 being relatively small. In such an event, the frame 22 is lifted and three of the cups 45 hold tightly and lift the plate 46, while the fourth cup 45, because .of leakage, lets, gp, The result is thatv one d corner vof the -pl-ate 46 hangs down and -is subject t9 damage or to causing damage to other things -as it is moved along. Y i

This problem lmay be solved by providing Aseparate pressureswitches 125, 126, 127, and 128 at each cup and by joiningthe'seswitches in series with each other and with-the starting device 130 for the motor20. Then, each cup '100 must have sufhcient vacuum inside it before its switch etc. will close. This means `that the cup 100 has to be fully engaged and at a predetermined vacuum, depending on the lifting conditions needed. Furthermore, the frame 22 is not lifted unless all four switches 125, 126, 127, and 1'28are closed. Thus lcornplete safety is assured.

To those skilled in the art to which this'in-vention'rre'- lates, -many changes lin construction and `widely differing embodiments and applications of .the invention will suggest themselves without departing lfrom the spirit and scope of the invention. The disclosures and the description herein are purely illustrative and are not iintended to be in any sense limiting.

What is claimed is:

1 In a crane for lifting and transporting steel plate and having a lifting frame, means to raise' said frame, and means to lower said frame, the combination -therewith of a Vplurality of suction vcup members; a resilient spring-mounted support for each suction cup member for securing it to said frame while permitting movement relative thereto; a limit switch secured to said frame adjacent one cup support for engagement 'by a portion lof said cup member, said vlimitswitch being so adjusted that its cup is lowered into contact .with 'the plate vand Iits spring is partially compressed before said limit switch reaches its engaging position; said limit switch then stopping saidmeans to lower said frame; means for applying suction to -the interior of said suction cups after engagement of said limit switch; a pressure-actuated switch adjacent each suction cup member for actuating said means to raise said frame when the correct Vacuum is present at each cup member, -said pressure switches 'being connected, in series so that all of them must be closed before the lframe is raised.

v2. In a crane for lifting and transporting steel plate, a lifting frame; means yto raise and lower said frame bevtween upper and lower limits; a limit switch determining the lower limit to which .said frame moves; four suction cup members .supported in pairs at oppositeends of said frame through a resilient spring-mounted support, said limit switch'being so adjusted that the cups are lowered into contact with the plate and the springs are partially compressed before said limit switch reaches its .engagingV position; means for rotating each pair between a position in line with said frame and a position transverse thereto, forpicking up narrow strips or wide ones; and means `for applying suction to the interior of said suction cups after engagement of said limit switch.

3. In fa crane for lifting and transporting steel plate, a lifting frame; means to raise and lower said frame between upper and lower limits; a limit switch determining the lower limit to which said frame moves; -a plurality of suction cup members supported by said frame through a resilient spring-mounted support, `said limit switch being so adjusted that the cups are lowered into contact with the plate and the springs are partially compressed before -said limit switch reaches its engaging position; means for applying suction to the interior of said suction oups after engagement of said limit switch; a plurality of pressure-actuated switch means, one for each cup, connected in series for actuating said means to'raise said frame only after a predetermined vacuum has been reached at all the cups.

4. In a crane for lifting and transporting steel plate, a lifting frame, means to raise and lower said frame between upper and lower limits; a limit switch determining the lower limit to which said frame moves; a plurality way of suction cup members supported by said frame through a resilient spring-mounted support, said limit switch being located on said frame adjacent one cup member for direct engagement by a projecting portion of said cup member upon a desired spring compression and so adjusted that the cups are lowered into Contact with the plate and the springs are partially compressed before said limit switch reaches its engaging position; and means for applying suction to the interior of said suction cups after engagement of said limit switch, thereby assuring engagement and partial flexing of all cups without exerting undue pressure on said plate.

5. In a crane for lifting and transporting steel plate, a lifting frame; means to raise and lower said frame; a plurality of suction cup members supported by said frame;

10 means for applying suction to the interior of said suction cups; a plurality of pressure-actuated switch means, one for each cup, connected in series for actuating said means to raise said frame only after a predetermined vacu has been reached at all said cups.

References Cited in the tile of this patent UNITED STATES PATENTS 1,228,690 Monnet June 5, 1917 1,525,147 Owen Feb. 3, 1925 2,049,850 Lytle et al. Aug. 4, 1936 2,665,013 Socke Jan. 5, 1954 FOREIGN PATENTS 247,603 Germany June 3, 1912 

